SYNOPSIS

DESCRIPTION

These functions generate the

ASN1

encoding of a string
in an

ASN1_TYPE

structure.

str contains the string to encode nconf or cnf contains
the optional configuration information where additional strings
will be read from. nconf will typically come from a config
file wherease cnf is obtained from an X509V3_CTX structure
which will typically be used by X509 v3 certificate extension
functions. cnf or nconf can be set to

NULL

if no additional
configuration will be used.

GENERATION STRING FORMAT

The actual data encoded is determined by the string str and
the configuration information. The general format of the string
is:

[modifier,]type[:value]

That is zero or more comma separated modifiers followed by a type
followed by an optional colon and a value. The formats of type,
value and modifier are explained below.

SUPPORTED TYPES

The supported types are listed below. Unless otherwise specified
only the

ASCII

format is permissible.

BOOLEAN

,

BOOL

This encodes a boolean type. The value string is mandatory and
should be

TRUE

or

FALSE

. Additionally

TRUE

, true, Y,
y,

YES

, yes,

FALSE

, false, N, n,

NO

and no
are acceptable.

NULL

Encode the

NULL

type, the value string must not be present.

INTEGER

,

INT

Encodes an

ASN1

INTEGER

type. The value string represents
the value of the integer, it can be prefaced by a minus sign and
is normally interpreted as a decimal value unless the prefix 0x
is included.

ENUMERATED

,

ENUM

Encodes the

ASN1

ENUMERATED

type, it is otherwise identical to

INTEGER

.

OBJECT

,

OID

Encodes an

ASN1

OBJECT IDENTIFIER

, the value string can be
a short name, a long name or numerical format.

UTCTIME

,

UTC

Encodes an

ASN1

UTCTime structure, the value should be in
the format

YYMMDDHHMMSSZ

.

GENERALIZEDTIME

,

GENTIME

Encodes an

ASN1

GeneralizedTime structure, the value should be in
the format

YYYYMMDDHHMMSSZ

.

OCTETSTRING

,

OCT

Encodes an

ASN1

OCTET STRING

. value represents the contents
of this structure, the format strings

ASCII

and

HEX

can be
used to specify the format of value.

BITSTRING

,

BITSTR

Encodes an

ASN1

BIT STRING

. value represents the contents
of this structure, the format strings

ASCII

,

HEX

and

BITLIST

can be used to specify the format of value.

If the format is anything other than

BITLIST

the number of unused
bits is set to zero.

UNIVERSALSTRING

,

UNIV

,

IA5

,

IA5STRING

,

UTF8

, UTF8String,

BMP

,

BMPSTRING

,

VISIBLESTRING

,

VISIBLE

,

PRINTABLESTRING

,

PRINTABLE

, T61, T61STRING,

TELETEXSTRING

, GeneralString,

NUMERICSTRING

,

NUMERIC

These encode the corresponding string types. value represents the
contents of this structure. The format can be

ASCII

or

UTF8

.

SEQUENCE

,

SEQ

,

SET

Formats the result as an

ASN1

SEQUENCE

or

SET

type. value
should be a section name which will contain the contents. The
field names in the section are ignored and the values are in the
generated string format. If value is absent then an empty

SEQUENCE

will be encoded.

MODIFIERS

Modifiers affect the following structure, they can be used to
add

EXPLICIT

or

IMPLICIT

tagging, add wrappers or to change
the string format of the final type and value. The supported
formats are documented below.

EXPLICIT

,

EXP

Add an explicit tag to the following structure. This string
should be followed by a colon and the tag value to use as a
decimal value.

By following the number with U, A, P or C

UNIVERSAL,
APPLICATION, PRIVATE

or

CONTEXT SPECIFIC

tagging can be used,
the default is

CONTEXT SPECIFIC.

IMPLICIT

,

IMP

This is the same as

EXPLICIT

except

IMPLICIT

tagging is used
instead.

OCTWRAP

,

SEQWRAP

,

SETWRAP

,

BITWRAP

The following structure is surrounded by an

OCTET STRING,

a

SEQUENCE,

a

SET

or a

BIT STRING

respectively. For a

BIT STRING

the number of unused
bits is set to zero.

FORMAT

This specifies the format of the ultimate value. It should be followed
by a colon and one of the strings

ASCII

,

UTF8

,

HEX

or

BITLIST

.

If no format specifier is included then

ASCII

is used. If

UTF8

is
specified then the value string must be a valid

UTF8

string. For

HEX

the
output must be a set of hex digits.

BITLIST

(which is only valid for a

BIT
STRING

) is a comma separated list of the indices of the set bits, all other
bits are zero.

This example produces an RSAPrivateKey structure, this is the
key contained in the file client.pem in all OpenSSL distributions
(note: the field names such as 'coeff' are ignored and are present just
for clarity):